Rotating turbomachine shafts are usually supported by means of bearings in a stationary casing. Seals are provided to prevent leakage of working fluid from a high pressure side to a low pressure side of the shaft. Recently, dry gas seals have been developed, which provide enhanced sealing against fluid leakages along the rotating shaft.
Dry gas seals are increasingly used as shaft seals in turbomachines, for example in centrifugal compressors, since they offer several advantages over other sealing arrangements. Dry gas seals as understood herein are shaft seals which have at least two sealing elements, herein referred to as sealing rings, which extend around the shaft in a circumferential direction, i.e. around the rotation axis of the shaft. One sealing ring is mounted for co-rotation with the shaft, while the other sealing ring is mounted stationary in the casing. Each sealing ring comprises a respective sealing surface pointing towards the oppositely arranged sealing ring. The stationary sealing ring and the rotating sealing ring are resiliently biased against each other and co-act at the sealing surfaces thereof. A pressurized dry gas is delivered between the sealing surfaces, such that a contactless sealing effect is obtained between the opposing sealing surfaces of the stationary and rotary sealing rings.
Dry gas seals are typically employed in centrifugal compressors. In some applications, heating arrangements are required, to prevent high molecular weight components of the seal gas from condensing, since the dry gas seals must be free of liquid to operate correctly. In other embodiments, heat removal arrangements have been developed, in order to prevent excessive heat built-up in the dry gas seals. Cooled dry gas seals are disclosed for instance in U.S. Pat. No. 8,814,508. A heat exchanger developing around the stationary sealing ring and the rotating sealing ring is provided. A liquid circulates in the heat exchanger to remove heat from the dry gas seal. This known dry seal arrangement operates satisfactorily, but is to some extent complex and cumbersome.
Therefore, there is still a need of improving shaft seal arrangements including dry gas seals, to provide safe, cost-effective and efficient seal arrangements, in particular in those applications where heat removal from the dry gas seal may become important.